1. Field of the Invention
This invention relates generally to the cleaning of optical elements in an excimer laser and more particularly to the cleaning of optical elements in situ using a carbon dioxide ice jet.
2. Discussion of Background
Various types of lasers have been developed in order to provide coherent light sources of different wavelengths. Excimer lasers are one type which are particularly valuable in that they are powerful ultraviolet sources. While their use previously was mostly in research, they are now becoming even more valuable in various materials processing areas. Excimer lasers use a mixture of gases which interact when excited by an electron beam or similar device. Thus, the mixture may include a combination of a halogen gas and one or more of the noble gases. For example, florine may be used with a mixture of argon and neon, a mixture of krypton and neon or a mixture of krypton and helium. Likewise chlorine may be used with a mixture of noble gases such as xenon and neon or xenon and helium.
One of the difficulties encountered in the use of an excimer laser is that the optics involved with the laser must be periodically cleaned. The optics usually involve a mirror or partially reflecting mirror at either end of the laser cavity. Various by-products are deposited on the optics in the course of operation of the device. Although the source of these deposits is not completely clear, they appear to involve impurities included in the gases, dust and other particulate matter and other by-products caused by the interaction of the gases. Since these deposits tend to absorb the ultraviolet light their presence reduces the power of the laser and must be periodically removed.
In the past, the optics have been cleaned by hand, that is by shutting down the laser, removing the mirrors and cleaning them with a solvent. The mirrors must then be replaced and realigned before the laser may be utilized again. This entire procedure may cause an interruption of an hour in the operation of the laser.